Neisseria meningitidis is a cause of bacterial meningitis. One approach to meningococcal vaccination relies on outer membrane vesicles (OMVs), as used in the Novartis MENZB™ product and the Norwegian Institute of Public Health MENBVAC™ product, both of which are generated by detergent treatment of meningococci.
It is known to change the protein composition of meningococcal outer membranes, and thus to change the composition of OMVs. Knockout of undesirable genes and over-expression of desirable genes have both been described. References 1-3 report pre-clinical studies of an OMV vaccine in which fHbp (also known as GNA1870) is over-expressed (and this over-expression can be combined with knockout of LpxL1 [4]). Reference 5 reported a clinical study of five formulations of an OMV vaccine in which PorA & FrpB are knocked-out and Hsf & TbpA are over-expressed. Reference 6 reports a phase I clinical study of a native outer membrane vesicle vaccine prepared from bacteria having inactivated synX and lpxL1 genes, over-expressed fHbp, two different PorA proteins and stabilised OpcA expression. Reference 7 reports a trivalent native outer membrane vesicle vaccine prepared from bacteria having inactivated synX and lpxL1 genes (and, in two cases, inactivated lgtA), two different PorA proteins, and over-expressed NadA or fHbp. Inactivation of genes such as lpxL1 is important if vesicles will be generated by methods which do not remove LPS.
These changes in protein composition can be effected in various ways. For instance, the bacteria can be growing under iron-limiting conditions in order to stimulate the expression of certain proteins related to iron metabolism. Other techniques can involve engineering the bacteria. For instance, reference 8 suggests that strong promoters (such as the porA, porB, lgtF, or hpuAB promoters) might be used to up-regulate expression of protective outer membrane proteins, or that suppressive transcription control mechanisms might be removed. Reference 9 suggests that genes can be engineered to remove their phase variability. The porA promoter was used in reference 7 to over-express NadA, whereas fHbp was over-expressed using the tac promoter.
It is an object of the invention to provide further and improved ways of modifying protein expression in meningococci, and in particular to provide promoters for driving expression of genes of interest. Up-regulation can be used to increase the levels of useful proteins in OMVs.